The present invention relates to an air dynamic bearing and, more particularly, to an air dynamic bearing constructed to prevent the inflow of a foreign substance.
An air dynamic bearing may be a hemispheric air dynamic bearing, a journal air dynamic bearing, or a thrust air dynamic bearing. The air dynamic bearing is used for a motor for driving a disk of a hard disk drive, a motor for driving a rotary polygon mirror of a laser printer or a laser scanner, or a motor for driving a head drum of a digital VCR which revolves at high speed.
In FIG. 1, a conventional hemispheric air dynamic bearing is illustrated. Referring to the drawing, the hemispheric air dynamic bearing includes an upper hemisphere 2 and a lower hemisphere 3, having their curved surfaces facing each other, which are fixed to a shaft 1, a bush 4 having hemispheric cavities 4a and 4b with which the upper hemisphere 2 and the lower hemisphere 3 are rotatably combined, a coupling ring 5 which confines the upper hemisphere 2 and the lower hemisphere 3 to the shaft 1, and a spacer 6 combined with the shaft 1, between the upper hemisphere 2 and the lower hemisphere 3, to maintain a clearance between the upper and lower hemispheres 2 and 3 and the bush 4.
The curved surfaces of the upper and lower hemispheres 2 and 3, and the surfaces of the bush 4 which face them, are lubricious and have grooves 7 formed in them. An appropriate clearance is maintained between the upper and lower hemispheres 2 and 3 and the bush 4. When the upper hemisphere 2 and the lower hemisphere 3 are rotated relative to the bush 4, an air pressure is generated in the clearance. The air pressure prevents the upper and lower hemispheres 2 and 3 from contacting the bush 4 while rotating.
However, there may be an inflow of a foreign substance from the outside into the clearance between the upper and lower hemispheres 2 and 3 and the bush 4. The inflow of the foreign substance into the clearance causes damage to the lubricious surfaces or degrades the rotational properties of the bearing.